phylogeny of the coral genus plesiastrea (cnidaria ... · contributions to zoology, 80 (4) 231-249...

Contributions to Zoology, 80 (4) 231-249 (2011)

Phylogeny of the coral genus Plesiastrea (Cnidaria, Scleractinia)

Francesca Benzoni1, 2, 4, Roberto Arrigoni2, Fabrizio Stefani2, Michel Pichon3

1 Institut de Recherche pour le Développement, UMR227 Coreus2, 101 Promenade Roger Laroque, BP A5, 98848 Noumea Cedex, New Caledonia2 Dept. of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy3 Museum of tropical Queensland, Townsville 4810, Australia 4 E-mail: [email protected]

Key words: COI, Plesiastrea versipora, Plesiastrea devantieri, rDNA, robust clade

Abstract

Until coral molecular phylogenies were published, the genus Plesiastrea was traditionally part of the family Faviidae and considered by several authors to be closely related to the genus Montastraea. However, genetic data has shown that Plesiastrea versipora, the genus type species, is evolutionarily distinct with-in the Robust clade of the Scleractinia and does not belong to the large clade grouping most representatives of the families Favii-dae, including Montastraea, Mussidae, Merulinidae, Trachy-phylliidae, and Pectiniidae. Instead, P. versipora is closely re-lated to non reef-dwelling taxa currently ascribed to the Oculi-nidae (Cyathelia axillaris) and Caryophylliidae (Trochocyathus efateensis). However, no discussion on the morphologic features of P. versipora compared to other taxa has been published yet. Moreover, no information is available about the phylogenetic placement of Plesiastrea devantieri, the only other species in the genus. The phylogeny of both Plesiastrea species was addressed through molecular analyses (COI and rDNA) and morphologi-cal analysis. Morphological differences between the two species included number of septa, cycles of vertical structures in front of the septa and septal micromorphology. On the basis of these data and nuclear and mitochondrial markers, P. devantieri belongs to the Faviidae-Merulinidae-Pectiniidae-Trachyphylliidae clade (Clade XVII sensu Fukami et al., 2008) and is most closely re-lated to Goniastrea aspera and G. palauensis. The type species of the genus Goniastrea, G. retiformis, however, is not closely related to either G. aspera and G. palauensis, or to P. devantieri. Taxonomic implications of these findings and morphologic af-finities between the two species and closely related taxa are dis-cussed.

Contents

Introduction .................................................................................... 231Material and methods ................................................................... 233 Sampling ................................................................................... 233 Specimenidentification .......................................................... 235 Museum collections and other examined specimens ....... 235 Morphologic analyses ............................................................ 235

DNA extraction,amplificationandsequencing ............... 235 Phylogenetic analyses ............................................................ 236Results ............................................................................................. 237 Macromorphology .................................................................. 237 Micromorphology ................................................................... 239 COI phylogeny ......................................................................... 239 rDNA phylogeny ...................................................................... 239Discussion ...................................................................................... 241 Polyphyly of the genus Plesiastrea ...................................... 241 Phylogenetic relationships of Plesiastrea versipora ........ 244 Phylogenetic relationships of Plesiastrea devantieri

and implications for taxonomy ............................................ 246Acknowledgements ...................................................................... 246References ...................................................................................... 247

Introduction

Scleractinian corals (Cnidaria, Scleractinia) belong to two main molecularly defined clades (Romano and Palumbi, 1996), the Robust and the Complex clade, and most families and genera as traditionally defined on the basis of skeleton macromorphologic characters are polyphyletic (Fukami et al., 2004, 2008; Benzoni et al., 2007; Nunes et al., 2008; Huang et al., 2009, 2011; Kitahara et al., 2010a). Moreover, Kitahara et al. (2010a) recently showed that azooxanthellate solitary corals from deep-water form a clade basal to both the Robust and the Complex corals. In other words, mo-lecular phylogenies of scleractinian corals and tradi-tional taxonomy and systematics based on skeleton morphology are, to a large extent, incompatible. Rec-onciliation of these two approaches is ongoing, but presently the need for an integrative approach which includes molecular, macrostructural, microstructural, reproductive and ecological analyses is required (Budd and Stolarski, 2009; Budd et al., 2010). In addition,

232 Benzoni et al. – Phylogeny of the coral genus Plesiastrea

shallow water, deep water, colonial, solitary, tropical and temperate taxa should all be included in the analy-ses to determine the evolutionary history of this an-cient group (Romano and Cairns, 2000; Le Goff-Vitry et al., 2003; Barbeitos et al., 2010; Kitahara et al., 2010b). One of the most challenging tasks in the taxonomy of the shallow water zooxanthellate corals is the revi-sion of the family Faviidae Gregory, 1900 which, to-gether with the Merulinidae Verrill 1866, Mussidae Ortmann, 1890, Trachyphyliidae Verrill, 1901, and Pectiniidae Vaughan and Wells, 1943, are found in the Robust clade (Fukami et al., 2004, 2008; Kitahara et al., 2010b). Despite a deep divergence between Atlan-tic and Indo-Pacific taxa in both the Mussidae and Faviidae (Fukami et al., 2004), most genera from these families were retrieved in several closely related clad-es. The genera Cladocora Ehrenberg, 1834, Oulastrea Milne-Edwards and Haime 1848, Leptastrea Milne-Edwards and Haime 1848, and Plesiastrea Milne-Ed-wards and Haime 1848, however, are not closely re-lated to the remainder of the Faviidae, nor to one an-other (Fukami et al., 2008; Barbeitos et al., 2010). Plesiastrea is clearly distinct and divergent from the rest of the Faviidae (Fukami et al., 2008). Despite strong morphologic affinities (Vaughan and Wells, 1943; Wells, 1956; Chevalier, 1971; Wijsman-Best, 1977; Veron et al., 1977; Chevalier and Beauvais, 1987), no close phylogenetic relationship has been found between Plesiastrea and the genus Montastraea de Blainville, 1830, the latter actually being polyphyl-etic (Fukami et al., 2004, 2008; Huang et al., 2009). Different vertically developed skeletal structures are found in the corallites of scleractinian corals. Their origin, structure, number, size, and shape have been used for taxonomy and systematics (Vaughan and Wells, 1943). The principal ones are the septa (radially arranged around the centre of the corallite) and, if pre-sent, the columella (found at the centre of the corallite) (Vaughan and Wells, 1943; Chevalier and Beauvais, 1987). In certain taxa a third type of vertical skeletal structure can exist between the inner margin of the septa and the columella. These, generally referred to as palar structures (PS), are arranged in one or more crowns surrounding the columella. In transverse sec-tion PS can be of different shape and size within the same corallite. Their origin and the process of forma-tion can be different. The term palus (pali) is used to refer to a pillar-like palar structure composed of its own system of divergent centers of rapid accretion (Stolarski, 2003) (formerly trabeculae), while a pali-

form lobe is a PS formed by a single center of rapid accretion stemming from the inner end of a septum (Chevalier and Beauvais, 1987). The genus Plesiastrea was originally described by Milne-Edwards and Haime (1848) on the basis of a specimen from the Indian Ocean named Astrea versi-pora by Lamarck (1816). The main characters of the genus were described as plocoid corallites, presence of pali sensu stricto, and the extracalicinal mode of coral-lite budding. The species Plesiastrea urvillei Milne-Edwards and Haime, 1849, and P. quatrefagiana Milne-Edwards and Haime, 1849, were also ascribed to the genus but both may be junior synonyms of P. versipora (Veron et al., 1977). According to Chevalier (1971) the main skeletal character distinguishing Ple-siastrea from the other genera is the presence of pali as opposed to paliform lobes in the other Faviidae such as, among the others, Montastraea and Goniastrea. Plesiastrea has presumably remained monotypic for decades until the description of P. devantieri on the basis of specimens from Socotra Island, Yemen (Ve-ron, 2000, 2002). In his original description Veron (2002) did not provide details on the micromorpho-logical characters of P. devantieri and species phylo-genetic relationships were not examined. Morphological affinities between Plesiastrea and Montastraea and nomenclatural confusion between the two taxa and Orbicella, a junior synonym of Mon-tastraea (Wijsman-Best, 1977) on the one hand, and Favia on the other hand, have been discussed by Wijs-man-Best (1977) and Veron et al. (1977) who provided detailed accounts of the history of nomenclatural con-fusion between those genera. Although Plesiastrea is superficially similar to Cyphastrea (Veron, 2002) no nomenclatural confusion occurred between the two taxa. Chevalier (1971) described transitional morphs between P. versipora and M. curta. The latter species was first ascribed to Orbicella by Dana (1846) and later moved to the genus Montastraea whose type spe-cies, Astrea guettardi Defrance, 1830, is a fossil. Ac-cording to Wijsman-Best (1977) some specimens identified as Orbicella by Yabe et al. (1936) would actually belong to Plesiastrea while specimens identi-fied by Wells (1954) as Plesiastrea would belong to Montastraea. Moreover, Wijsman-Best (1977) recog-nised transitional forms between P. versipora and an-other Montastraea species, M. annuligera (cf. holo-type illustrated in Veron et al., 1977, p. 141, Fig. 267). Vaughan and Wells (1943) in their description of the genus, indicated that Plesiastrea was like Favia, but with extracalicinal budding, as opposed to intracalici-

233Contributions to Zoology, 80 (4) – 2011

nal. It was Chevalier (1971) who finally suggested that the presence of true pali instead of paliform lobes and the absence of directive mesenteries would be suffi-cient to separate Plesiastrea from any species ascribed to the genus Montastraea. Later, molecular data sup-ported this separation (Fukami et al., 2004). No close relative of Plesiastrea versipora was ap-parent until Kitahara et al. (2010b) included several azooxanthellate and deep water taxa in their phyloge-netic analyses of the Scleractinia. In their COI phylog-eny a close phylogenetic relationship between P. ver-sipora and Trochocyathus efateensis Cairns, 1999 (tra-ditionally in the Caryophylliidae Dana, 1846) and Cy-athelia axillaris (Ellis and Solander, 1786) (currently in the Oculinidae Gray, 1847) was suggested. To date, no morphological analyses have been performed to re-vise the micro-morphology of P. versipora in light of these molecular results. Finally, the phylogenetic rela-tionships between P. versipora and P. devantieri Ve-ron, 2002 have not been investigated. In this paper morphologic and molecular analyses of P. versipora and P. devantieri were performed to

ascertain the phylogenetic relationships, first, between the two congeneric species, and, second, with the Faviidae in general.

Material and methods

Sampling

Sampling took place at several localities in the Indian Ocean and Gulf of Aden (Table 1). Specimens of Plesi-astrea versipora for morphological and molecular anal-yses were sampled along the Gulf of Aden coasts of Yemen, in Socotra and Mayotte. Plesiastrea devantieri was sampled in Socotra (type locality) and in Mayotte. The Goniastrea retiformis (Lamarck, 1816) and Mon-tastraea curta (Dana, 1846) specimens included in the molecular analyses and illustrated in Fig. 1 were col-lected in Balhaf, Yemen, and Socotra, respectively. Sam-pling in Yemen and Socotra was performed between 2007 and 2010 within the frame of the Yemen Sclerac-tinia Biodiversity Project supported by TOTAL SA.

Table 1. List of the material collected for this study and housed at the University of Milano-Bicocca (UNIMIB) collection. BI = Bir Ali (Gulf of Aden, Yemen); SO = Socotra Island (Indian Ocean, Yemen); KA = Kamaran Island (Red Sea, Yemen); MY = Mayotte Island (Indian Ocean, France); FB = F. Benzoni; MP = M. Pichon; SM = S. Montano; AC = A. Caragnano.

UNIMIB code Genus species collector rDNA COI

BAL 178 Plesiastrea versipora FB, MP BAL 214 Plesiastrea versipora FB, MP Y719 Plesiastrea versipora FB FR837995 FR837985MU010 Plesiastrea versipora FB, MP MU111 Plesiastrea versipora FB, MP MU146 Plesiastrea versipora FB, MP FR837996 FR837986MU169 Plesiastrea versipora FB, MP BA123 Plesiastrea versipora FB, SM FR837994 FR837984AD021 Plesiastrea versipora FB, MP KA124 Plesiastrea versipora FB, AC SO115 Plesiastrea versipora FB, MP MY343 Plesiastrea versipora FB SO024 Plesiastrea devantieri FB, MP FR837997 FR837987SO031 Plesiastrea devantieri FB, MP FR837998 FR837988SO093 Plesiastrea devantieri FB, MP FR837999 FR837989MY003 Plesiastrea devantieri FB MY004 Plesiastrea devantieri FB MY053 Plesiastrea devantieri FB MY064 Plesiastrea devantieri FB MY139 Plesiastrea devantieri FB SO041 Montastraea curta FB FR838000 FR837990BA024 Goniastrea retiformis FB, SM FR837991 FR837981BA077 Goniastrea retiformis FB, SM FR837992 FR837982SO070 Goniastrea retiformis FB, MP FR837993 FR837983


Sampling in Mayotte took place in May 2010 during the third Reef leg of the Tara Oceans scientific expedition. Digital images of living corals in the field were tak-en with a Canon G9 in an Ikelite underwater housing system. Coral specimens were collected, tagged, and for each specimen 1 cm2 was broken off the colony and

preserved in absolute ethanol for further molecular analysis. The remaining corallum was placed for 48 hours in sodium hypochlorite to remove all soft parts, rinsed in freshwater and dried for microscope observa-tion. Images of the cleaned skeletons were taken with a Canon G9 digital camera.

Fig. 1. Morphology of type material and exam-ined specimens of: Plesiastrea versipora A) holotype MNHN 36, and B) specimen MU146; Plesiastrea devantieri C) holotype MTQ G 55847 (Picture by P. Muir, MTQ), and D) speci-men SO031; Montastraea curta E) syntype USNM 14 (Picture by the National Museum of Natural History, Smithsonian Institution), and F) specimen SO041; Goniastrea retiformis G) Holotype MNHN 86, and H) specimen BA077. Scale bars = 1 cm. Grey filled arrows in inset of C show third order septa (S3) in P. devantieri holotype.

Type material Examined material


Specimenidentification

The material collected was identified referring to the genera and species descriptions and illustrations by Lamarck (1816), Dana (1846), Milne-Edwards and Haime (1848), Vaughan and Wells (1943), Wijsman-Best (1976, 1977), Veron et al. (1977), Chevalier and Beauvais (1987), and Veron (2000, 2002). Moreover, the type specimens of Plesiastrea versipora (Fig. 1A), P. devantieri (Fig. 1C), Montastraea curta (Fig. 1E), and Goniastrea retiformis (Fig. 1G) were examined and their morphology compared with that of the mate-rial sampled for this study (Fig. 1B, D, F, and H, re-spectively).

Museum collections and other examined specimens

Type material and specimens examined for this study are deposited in different institutes.

Abbreviations:EPA Environment Protection Authority, Sana’a

and Socotra, YemenIRD Institut de Recherche pour le Développe-

ment, Nouméa, New CaledoniaMNHN Muséum National d’Histoire Naturelle, Paris,

FranceMTQ Museum of Tropical Queensland, Towns-

ville, AustraliaSMF Senckenberg Museum, Frankfurt, GermanyUNIMIB Università di Milano-Bicocca, Milan, ItalyUSNM United States National Museum of Natural

History, Washington, U.S.A.

The holotype of Plesiastrea devantieri (MTQ G 55847) was examined at the Museum of Tropical Queensland. The P. versipora specimens in the Lamarck and Milne-Edwards collections hosted at MNHN, in-cluding the species holotype, as well as the type mate-rial of Plesiastrea urvillei (MNHN 773), Astrea reti-formis (MNHN 86), and Heliastrea annuligera Milne-Edwards and Haime, 1848 (MNHN 674), were exam-ined during a visit in October 2010. Images of the lat-ter were kindly taken by A. Andouche (MNHN). The U.S Exploring Expedition specimens at the USNM were examined during a visit in July 2009. The illus-tration of the one of the syntypes of Astraea (Orbicel-la) curta (USNM 14) was provided with the permis-sion of the National Museum of Natural History, Smithsonian Institution, (http://www.nmnh.si.edu/). Plesiastrea spp. and Cyathelia cf axillaris specimens

in the SMF Socotra collection currently deposited at the Yemen EPA Socotra were studied in February 2010. The images of Trochocyathus efateensis were kindly provided by M. Kitahara (James Cook Univer-sity).

Morphological analyses

Both macro and micromorphological characters (sensu Budd and Stolarski, 2009) of the two Plesiastrea spe-cies were examined using light microscopy (Zeiss Stemi DV4 stereo-microscope) and SEM, respective-ly. For SEM, specimens were mounted using silver glue, sputter-coated with conductive gold film and ex-amined using a Vega Tescan Scanning Electron Micro-scope at the SEM Laboratory, University of Milano-Bicocca.

DNA extraction,amplificationandsequencing

Extraction of coral DNA was performed using DNeasy® Tissue kit (QIAGEN, Qiagen Inc., Valencia, CA, USA) according to the manufacturer’s protocol. Each extracted sample was quantified using a Nan-odrop 1000 spectrophotometer (Thermo Scientific) and diluted to a final DNA concentration of 3ng/µl. The mitochondrial gene COI and a portion of rDNA (spanning the entire ITS1, 5.8S, ITS2 and a portion of 28S and 18S) were amplified and sequenced. COI and rDNA have been extensively used to reconstruct phy-logenetic relationships among scleractinians corals (Odorico and Miller, 1997; Lam and Morton, 2003; Fukami et al., 2004, 2008; Moothien Pillay et al., 2006; Benzoni et al., 2007, 2010; Stefani et al., 2008; Huang et al., 2009; Kitahara et al., 2010b). The use of both markers allowed inference of the phylogeny at higher and lower systematic levels, due to their differ-ent evolutionary rates (Shearer et al., 2002; Chen et al., 2004; Wei et al., 2006; Huang et al., 2008). The mitochondrial marker was amplified using specific primers for Scleractinia, MCOIF (5’ TCT ACA AAT CAT AAA GAC ATA GG 3’) and MCOIR (5’ GAG AAA TTA TAC CAA AAC CAG G 3’) (Fukami et al., 2004). The 50 μl PCR mix was composed of 1X PCR buffer, 2 mM MgCl2, 0.3 μM for both of each primer, 0.01 mM dNTP, 3 U taq polymerase (Sigma-Aldrich Co., St. Louis, MO, USA) and 8 μl of DNA solution. The thermal cycle consisted of an initial denaturation phase of 94°C for 2 min followed by 30 cycles com-posed of 94°C for 45 sec, 55°C for 45 sec, 72°C for 90 sec, and finally an extension phase at 72°C for 5 min.


Amplification of nuclear marker was performed using the coral-specific primer A18S (5’ GAT CGA ACG GTT TAG TGA GG 3’) (Takabayashi et al., 1998) and the universal primer ITS4 (5’ TCC TCC GCT TAT TGA TAT GC 3’) (White et al., 1990). Reactions were conducted with 1X PCR buffer, 2 mM MgCl2, 0.4 μM for both of each primer, 0.1 mM dNTP, 2 U taq poly-merase (Sigma-Aldrich Co., St. Louis, MO, USA), 8 μl of DNA solution and water to 50 μl, using the pro-tocol of 96°C for 2 min, 30 cycles of 96°C for 10 sec, 50°C for 30 sec, 72°C for 4 min, ending with 72°C for 5 min. PCR products were sent to Macrogen Inc. (Seoul, South Korea) for further purification and se-quencing.

Phylogenetic analyses

Chromatograms were manually checked using Codon-Code Aligner 2.0.6 (CodonCode Corporation, Ded-ham, MA, USA). Sequences were aligned with BioEd-it Sequence Alignment Editor 7.0.9.1 (Hall, 1999). In-variable, polymorphic and parsimony informative sites were detected with DnaSP 5.10.01 software (Lib-rado and Rozas, 2009). Genetic distances and their

standard deviation were calculated as p-distance with MEGA 4.0.2 software (Tamura et al., 2007). Phyloge-netic inference was conducted using Bayesian Infer-ence (BI) with MrBayes 3.1.2 (Huelsenbeck and Ron-quist, 2001; Ronquist and Huelsenbeck, 2003), Maxi-mum Likelihood (ML) using PhyML 3.0 (Guindon and Gascuel, 2003) and Maximum Parsimony (MP) based on PAUP* 4.0b10 (Swofford, 2003). For BI and ML analyses evolutionary models were assessed with Akaike Information Criterion (AIC) as implemented in MrModeltest 2.3 software (Nylander, 2004). As most suitable models AIC selected the HKY+I+G for the mitochondrial marker (gamma=1.0033 and p-in-var=0.5341) and the GTR+I+G for the nuclear marker (gamma=1.0079 and p-invar=0.2315). BI analysis consisted of four parallel Markov chains implemented for 10500000 generations for COI (1000000 genera-tions for rDNA), saving a tree every 100 generations for both mitochondrial and nuclear markers and dis-carding the first 26251 trees as burn-in for COI (2501 for rDNA). For both markers BI analyses were stopped when the standard deviations of split frequencies were <0.01. The software Tracer 1.5 (Drummond and Ram-baut, 2007) was also used in order to correctly estimate

Fig. 2. In situ images of living colonies of: Plesiastrea versipora A) massive colony with typical green colouration, Kamaran Is-land, Yemen, 8 m; B) encrusting colony with brown colouration, Balhaf, Yemen; Plesias-trea devantieri C) massive colony, Socotra Island, 10 m. Close ups of the corallites of D) P. versipora with expanded polyps and E) P. devantieri.


the burn-in and to verify the convergence. Best ML tree was obtained with PhylML (HKY85 model for COI and GTR model for rDNA, 4 substitution rate cat-egories, setting the proportion of invariable sites and gamma distribution parameter to the values estimated with MrModeltest 2.3) using Shimodaira and Hase-gawa (SH-like) test to check the support of each inter-nal branch. MP analysis was performed using a heuris-tic search and the tree-bisection-reconnection branch swapping algorithm producing a strict consensus tree. Node supports were obtained with 500 bootstrap repli-cates in which the maximum number of trees was set to 40000.

Results

Macromorphology

Plesiastrea versipora and P. devantieri share macro-morphological traits such as a flattened to massive colony (Fig. 2A-C), plocoid corallite arrangement (Fig. 1A-D, 2D-E), the presence of three orders of laminar septa continuing over the wall as costae (Fig. 3, 4A-B) and well developed palar structures (Figs 3-4). The two species can be distinguished, however, on the basis of several macro and micromorphological

features (Table 2). Corallites are smaller in P. versi-pora (2 to 3.5 mm in diameter) (Fig. 1A-B) than in P. devantieri (3 to 5 mm in diameter) (Fig. 1C-D). Al-though both species have three cycles of septa (S1-3) and well developed palar structures, their number and development is substantially different in the two taxa (Table 2). In P. versipora S1 (6 to 8 septa) and S2 (6 to 8 septa) can be equal (Fig. 3A), or S2 variably shorter than S1 (Fig. 1A). Although in the holotype S1 and S2 can be 8 in most corallites (Fig. 1A), specimens bear-ing 6 S1 and S2 are commonly observed (Fig. 1A; [Figs. 284-292] Veron and Pichon, 1976). S3 can be up to ¼ the length of S1 (Fig. 3C), or extremely reduced (S1≥S2>S3). S1 always reaches the columella, S2 only if as developed S1. Two crowns of pali (P1-2) (12 - 16 pali in total) are present between S1-2 and the columella (Figs 3A, C, 4A, C). P1 and P2 can be equal (Fig. 4C) or sub-equal (Veron et al., 1977) and are very variable in width and length (see Veron et al., 1977, p. 151, Figs. 284-292). P1-2 flush with, or slightly higher than, the corallite wall upper margin (Fig. 4A). In P. devantieri S1 usually number 6 to 8 in mature corallites and reach the columella (Fig. 3B). In this spe-cies palar structures are actually paliform lobes, not pali, and number 8 in most corallites (Figs 3B, D, 4D). S2 are often incomplete, usually ¼ to ½ of the first order in length. No paliform lobe development occurs be-tween S2 and the columella (Fig. 3B, D). Occasionally,

Table 2. Morphological characters distinguishing Plesiastrea versipora from P. devantieri.

Character P. versipora P. devantieri

Corallite diameter 2 - 3.5 mm 3 - 5 mm Orders of septa (S) 3 3 S1 6 - 8 reaching the fossa 6 - 8 reaching the fossa S2 6 - 8 £ S1 6 - 8, £ S1 S3 12 - 16 < S1-2 12 - 16 < S1-2 Type of palar structures Pali Paliform lobes Crowns of palar structures (PS) 2 1 PS1 6 - 8 6 - 8 PS2 6 - Columella Papillose Spongy

Septum margin ornamentation Rounded to pointed granules regularly Paddle-shaped teeth arranged along the main axis Shape of palar structures Round to oval Oval to wedge shaped (transverse section) Granulation arrangement of Linearly arranged along the main axis Radially arranged palar structures Height of the palar structures Flush with the corallite wall upper Between the columella and the corallite margin wall upper margin

Mic

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Fig. 3. Scanning Electron Micrograph of a corallite of A) Plesiastrea versipora (BA123) and of B) Plesiastrea devantieri (TO-MAY053) showing septal arrangement. De-tails of septa and palar structures (PS) in C) P. versipora (MU146) and D) P. devantieri. I = PS in front of first order septa; II = PS in front of second order septa.

Fig. 4. Scanning Electron Microscope side view of a corallite of A) Plesiastrea versipo-ra (BA123) and of B) Plesiastrea devantieri (TO-MAY053) showing different height of the palar structures in the two species. Ar-rangement and shape of C) pali P. versipora (BA123) and D) paliform lobes in P. devan-tieri.


one or two longer secondary septa can almost reach the columella but these remain devoid of paliform lobes. Although not mentioned in the species original description, a third order of septa is also present in the holotype (inset in Fig. 1C) as well as in the rest of the examined material. S3 generally much reduced (Fig. 3B, D) and hard to detect with the naked eye (Fig. 1C-D). Although Veron (2002) indicated in the P. devan-tieri original description that costae do not extend over the coenosteum in the holotype, this was observed in parts of the specimen, and in a number of specimens where the coenosteum between corallites is more de-veloped costae show a tendency to extend over it (Fig. 1D). The paliform lobes between S1 and the columella sit in the fossa, lower than the corallite wall upper mar-gin level (Fig. 4B). The columella in P. versipora is always well devel-oped although small and papillose (Fig. 4C). In P. devantieri the columella is made of a few interwoven threads (Fig. 4D).

Micromorphology

SEM observations of septal micromorphology showed remarkable differences between the two examined species. In P. versipora minute, regularly spaced sep-tal teeth are arranged along the septum direction (Fig. 5A, C). Conversely, in P. devantieri the typical pad-dle-like structures or fans described in the Atlantic Faviidae (Cuif and Perrin, 1999; Cuif et al., 2003) but not in the Pacific Faviidae (Budd and Stolarski, 2011) are observed (Fig. 5B, D). These distinct spiked ridges perpendicular to the septal plane (Budd and Stolarski, 2009) were also observed on the costae (Fig. 5B). The septa centers of rapid accretion in P. versipora are formed by calcification axes inclining outwards from the centers of rapid accretion axis and producing a granulation pattern on the septal sides (Fig. 6A). The granules are arranged in vertical lines and the degree to which they protrude may vary between corallites and specimens (Fig. 3C) or less (Fig. 5A, C). In P. devantieri granulations on the septa sides are similar though less regularly arranged and the lines are further apart (Fig. 6B). Finally, shape and ornamentation of the palar struc-tures differ between P. versipora and P. devantieri. In P. versipora pali can be elongate to wedge-shaped in transverse section (Fig. 4C), their main axis following the same direction as the septum behind it. Granula-tions are regularly arranged along the palus main axis (Fig. 6A, C) in the same fashion as along the septum.

Paliform lobes in P. devantieri are round to oval in transverse section (Fig. 4D) and their ornamentation is star-like (Fig. 6B, D), closely resembling in shape and ornamentation the septal teeth formed by calcification axes in multiple directions as illustrated by Budd and Stolarski (2009, cf. Fig. 6) in the Mussidae.

COI phylogeny

Three specimens of Plesiastrea versipora and three of P. devantieri were sequenced and used for phyloge-netic reconstruction, together with 51 sequences from clades XI to XXI delineated in Fukami et al. (2008) and other sequences from Kitahara et al. (2010b). In particular, the available sequences of Trochocyathus efateensis, Cyathelia axillaris and Plerogyra sp. were added. A sequence of Galaxea fascicularis (AB441201) was included as an outgroup. Finally, three sequences of Goniastrea retiformis and one of Montastraea curta from the Indian Ocean were also obtained during this study and added to the dataset. The final alignment consisted of 580 positions. No indels were observed and a total of 185 polymorphic sites (112 informative) were identified. The phyloge-netic trees obtained under the three criteria are largely congruent between each other and with the main avail-able phylogenies. In detail, clades XII, XIII, XIV, XV, XVIII, and XXI sensu Fukami et al. (2008) are re-solved. Clade XI is partially unresolved, due to the ba-sal unresolved position of Oulastrea crispata. Clade XVII, also includes subclade XVIII. Finally, clade XIX and XX merged in a single clade. The phylogeny shows low resolution at genus and species levels, as extensive polytomies affect clade XVII in particular. The three examined specimens of P. devantieri are not resolved within this main clade. Nevertheless, Plesias-trea versipora samples from the Gulf of Aden and the Indian Ocean cluster together with the other specimens from the Western Pacific, with C. axillaris, and T. efa-teensis in a sister clade, thus confirming the strong af-finity between these genera as indicated by Kitahara et al. (2010b). Overall, the genus Plesiastrea results polyphyletic and a strong divergence between the two species ascribed to this genus is supported by the mito-chondrial marker.

rDNA phylogeny

A total of three specimens of Plesiastrea versipora and three of P. devantieri were amplified, sequenced and used in the phylogenetic analysis. No intraindividual


Fig. 5. Scanning Electron Microscope imag-es of A, C) Plesiastrea versipora (MU146) and B, D) Plesiastrea devantieri (TO-MAY053) septa showing different types of ornamentation in the two species. Grey filled arrows point at granules; white filled arrows point at paddle-shaped teeth; white dashed lines indicate the septal plane direction; grey dashed line indicates the paddle-shaped teeth main axis direction.

Fig. 6. Scanning Electron Microscope lateral views of septa and palar structures of A) Ple-siastrea versipora (MU146) and B) Plesias-trea devantieri (TO-MAY053). White dotted insets indicate the position of elements shown in C and D, respectively. Top view of C) two pali of P. versipora and D) one pali-form lobe in P. devantieri showing different arrangement of granules in the two species. Larger dashed white arrows indicate the sep-tal plane direction, smaller dashed grey ar-rows indicate the granules growth directions.


polymorphisms were observed in the chromatograms. Although direct sequencing of rDNA in corals may hide some rare intra-individual variants (Vollmer and Palumbi, 2004), this loss of information may be rele-vant only in a limited number of cases in the Complex clade (Marquez et al., 2003; Vollmer and Palumbi, 2004; Chen et al., 2004), and direct sequencing pre-vents the risk of introducing PCR artefacts into the analysis, unlike methods using cloning (Bradley and Hillis, 1997; Flot et al., 2006). The phylogenetic relationships between the ob-tained sequences and 42 other sequences, congruent with those employed for the mitochondrial phylogeny, were then inferred. Unfortunately, no sequences of C. axillaris or T. efateensis were available. Sequences of Goniastrea retiformis were obtained and included, to-gether with the homolog and congeneric sequences of Goniastrea palauensis and Goniastrea aspera availa-ble in Genbank. The final alignment consisted of 763 bp, with 384 positions showing indels. A total of 177 polymorphic sites (127 parsimony informative) were detected. The reconstructions obtained according to the three criteria are largely congruent. Minor variations are due to the lack of resolution in a few nodes shown by the MP analysis. Overall, the clades XI, XIV, XV sensu Fukami et al. (2008) detected in the mitochondrial tree are retained in the rDNA phylogeny, but here a higher resolution at species and genus levels is observed. Clades XIX and XX sensu Fukami et al. (2008) merge in a single clade, while clade XVIII form a subclade within the main XVII clade. Plesiastrea versipora clusters with P. lichtensteini, thus supporting the relationships shown by the mito-chondrial phylogeny. Plesiastrea devantieri falls with-in clade XVII, as seen in the COI phylogeny. A close affinity of P. devantieri with a clade clustering togeth-er G.palauensis and G. aspera is shown. The type spe-cies of the genus Goniastrea, G. retiformis, groups to-gether with Scapophyllia cylindrica and is more close-ly related to Montastraea curta and Platygyra sinensis than to the other two congeneric species.

Discussion

Polyphyly of the genus Plesiastrea

Plesiastrea versipora is a well known widely distrib-uted Indo-Pacific species that has been recognised and identified for almost two centuries (inter alia Lamarck,

1816; Milne-Edwards and Haime, 1849; Yabe et al., 1936; Wells, 1954; Chevalier, 1971; Wijsman-Best, 1977; Veron et al., 1977; Scheer and Pillai, 1983; Car-penter et al., 1997; Veron, 2000; Pichon et al., 2010). The nomenclatural history of P. versipora is well sum-marised in Veron et al. (1977 [Figs 284-292]), together with a series of illustrations of the species morpholog-ical variability (see also Scheer and Pillai, 1983 [Plate 33, Figs 2-5]). The specimens examined in this study fall within the range of variability previously docu-mented. Conversely, P. devantieri is a relatively newly described species recorded from Socotra and Mada-gascar (Veron, 2002). Only a few illustrations (Veron, 2000, 2002) and deposited specimens of P. devantieri are available. Sampling for this study in the type local-ity, as well as in another locality of the Indian Ocean, Mayotte (new geographic record for the species), pro-vided material to evaluate the extent of intraspecific variability of certain characters and the stability of oth-ers. On the basis of the material examined there are superficial similarities between the two species. How-ever, closer examination of the septal and palar macro and micromorphology together with molecular analy-ses using two independent markers indicates that P. versipora and P. devantieri are not phylogenetically closely related, and the latter shares more characters with the so-called ‘Bigmessidae’ (sensu Huang et al., 2011) than with Plesiastrea. Our molecular results indicate a divergence level, expressed as p-distance, of 22.1 ± 1.7 % (mean ± s.d.) for the rDNA marker and 5.4 ± 0.9 % for the COI marker. In the case of rDNA the divergence is compa-rable to the estimates obtained for some of the most polyphyletic and divergent genera, such as Montast-raea and Platygyra (Wei et al., 2006). Also the p-dis-tance obtained from the COI region is close to the up-per distribution limit of confamilial divergences within the Scleractinia (Shearer and Coffroth, 2008). From a morphological standpoint, the differences between P. versipora and P. devantieri are consistent and exceed the variation normally observed between closely related (i.e. congeneric) species of hard corals (i.e. variations in corallite diameter, length of septa, number of cycles of septa, number of septa in a cycle). Differences in the septal margin ornamentation and palar structures between these species support the non-monophyly of the two taxa at the genus level. The distribution of the calcification centres controls the septal external micro-morphology and the forma-tion of teeth (Cuif and Perrin, 1999). In the Faviidae the teeth shape and structure, and the organization of


Fig. 7. Phylogenetic tree of mitochondrial gene COI reconstructed with Bayesian Inference. Maximum Likelihood and Maximum par-simony detected similar topologies. Numbers at each node show percentages of (above) Sh-like support (>70%), and MP bootstrap (>50%), and (below) Bayesian posterior probability (>70%); - = no support. Clades of Plesiastrea versipora and Plesiastrea devantieri are in bold. Clade numbers refer to the same clades previously identified by Fukami et al. (2008).

P. versipora

P. devantieri

0.4

AB441224 Fungia scutaria

AB117297 Meandrina braziliensis

AB117244 Symphyllia recta

AB289562 Physogyra lichtensteini

EU371660 Diploastrea heliopora

SO031 Plesiastrea devantieriSO093 Plesiastrea devantieri

AB117293 Oculina diffusa

AY451349 Diploria strigosa

HM018622 Cyathelia axillaris

AB117239 Mussa angulosa

AY451352 Montastraea annularis

EU371687 Favites abdita

AY451357 Montastraea faveolata

EU371658 Acanthastrea echinata

SO070 Goniastrea retiformis

BA123 Plesiastrea versipora

HM018662 Platygyra sinensis

DQ643832 Astrangia sp

AB117386 Pectinia paeonia

EU37170 Goniastrea retiformis

AB117241 Lobophyllia corymbosa

SO024 Plesiastrea devantieri

FJ345428 Favia rotumana

EU371699 Goniastrea palauensis

HM018667 Trochocyathus efateensis

AY451359 Solenastrea bournoni

AY451358 Montastraea franksi

SO041 Montastrea curta

AB441201 Galaxea fascicularis

AB289563 Blastomussa wellsi

AY451351 Favia fragum

FJ345413 Barabattoia amicorum

AB117238 Isophyllia sinuosa

AB117281 Platygyra daedalea

AB117252 Echinophyllia aspera

AB441210 Coscinaraea columna

AB289561 Plesiastrea versipora

EU371702 Leptastrea purpurea

AY451360 Dichocoenia stokesiAB117299 Dendrogyra cylindrus

EU371706 Montastraea curta

HM018663 Plerogyra sp

FJ345416 Cyphastrea microphthalma

FJ345444 Scapophyllia cylindrica

EU371673 Favia matthaii

AB117292 Cladocora arbuscula

MU146 Plesiastrea versipora

EU371688 Favites chinensis

BA077 Goniastrea retiformis

FJ345430 Goniastrea aspera

FJ345435 Oulastrea crispata

Y719 Plesiastrea versipora

FJ345439 Oulophyllia crispa


AB117294 Eusmilia fastigiata

HM018650 Heliofungia sp.93/99100

86/81100

95/9799

97/99100

92/8585

90/8810085/55

88

96/10010094/96

100

99/9699

91/10099

87/8798

87/7677

83/8679

86/6682

91/5492 98/99

100

93/97100

95/7595

96/97100

95/97100

91/8199

91/8591

98/10099

94/9799

92/5870

74/6975

77/-95

84/-81

-/79-

91/8570

98/10097

XIII

XI

XIV

XII

XIX-XX

XXI

V

XV

AB441199 Acanthastrea hillaeAB441200 Micromussa amakusensis

97/9699 XVIII

XVII


Fig. 8. Phylogenetic tree of a portion of rDNA (spanning the entire ITS1, 5.8S, ITS2 and a portion of 28S and 18S) reconstructed with Bayesian Inference. Maximum Likelihood and Maximum Parsimony detected similar topologies. Numbers at each node show percent-ages of (above) SH-like support (>70%), and MP bootstrap (>50%), and (below) Bayesian posterior probability (>70%); - = no support. Clades of Plesiastrea versipora and Plesiastrea devantieri are in bold. Clade codes refer to the same sub-clades previously identified by Huang et al. (2011).

0.2

AY509724 Diploastrea heliopora

AY722775 Montastraea curta

AB441403 Micromussa amakusensis

AF481897 Platygyra sinensis

AY722781 Oulastrea crispata

AB065302 Montastraea annularis

AY722755 Favites abdita

AY722740 Acanthastrea echinataAB441401 Acanthastrea echinata

AY722750 Cyphastrea japonica

SO093 Plesiastrea devantieri

EU149831 Fungia scutaria


AY722763 Goniastrea sp

AY722771 Hydnophora exesa

AY722768 Goniastrea palauensis

AY722774 Montastraea curtaSO041 Montastraea curta

AB441405 Physogyra lichtensteini

SCU65479 Scapophyllia cylindrica

AB065326 Montastraea annularis

AY722759 Goniastrea aspera

AY722751 Cyphastrea japonica

MU146 Plesiastrea versipora

SO070 Goniastrea retiformisAY722765 Galaxea fascicularis

AB441399 Solenastrea bournoni

AB441402 Mussa angulosa

AY722756 Favites abdita

AF483780 Plesiastrea versipora

AY722770 Hydnophora exesa

MFU60605 franksiMontastraea

AB214160 Platygyra sp

Y719 Plesiastrea versipora

BA123 Plesiastrea versipora

AB441398 Plesiastrea versipora

AY509729 Diploastrea heliopora

AF013731 faveolataMontastraea

AY722761 Goniastrea aspera

AF013733 Montastraea faveolata


AF483798 Plesiastrea versipora

AB065360 Montastraea franksi

AY722767 Goniastrea palauensis

AB441406 Coscinaraea columna

EU149830 Fungia scutaria

AF481901 Platygyra sinensis

SO031 Plesiastrea devantieriSO024 Plesiastrea devantieri

AB441400 Echinophyllia aspera

80/9975

70/10075

70/-76

92/93100

100/100100

100/100100

77/6194

100/100100

100/100100

100/99100

90/98100

94/100100

89/-98

93/94100

92/99100

95/8592

91/70100

73/6795

81/-82

97/100100

100/100100

100/100100

100/99100

71/6497

98/100100

100/100100

78/7986

98/-93

88/-93

90/-92

100/8096

89/-98

89/6495

100/100100

100/-80

95/91100

P. versipora

XV

XVII-C

XVII-HXVII-F

XVII-G

XVII-B

XVII-A

XVII-C

P. devantieri


the granules are variable and different between Atlan-tic and Pacific taxa (Budd and Stolarski, 2011). In the Atlantic Faviidae the septal calcification centres are arranged in clusters giving typical ‘paddle-shaped’ teeth (Figs 4-6 in Cuif and Perrin, 1999; Budd and Sto-larski, 2011). Following the definition given by Budd and Stolarski (2009) ‘a paddle-shaped tooth is formed by a short series of calcification centres (a secondary calcification axis) that is transverse to the direction of the septal plane’. Paddles are separated by short septal zones in which centres occur in the median septal plan. In the Pacific Faviidae septal teeth are multidirection-al, more irregular and spine-like or ‘lacerate’ (Budd and Stolarski, 2011 [Fig. 2]). In P. versipora septal teeth are regularly arranged along the septum direc-tion. In this species, the septal ornamentation and mi-cro-structure are devoid of septal paddles, and similar to that described by Cuif et al. (2003) for Cladocora caespitosa, another taxon previously included by some authors in the Faviidae and currently in need of revi-sion. Conversely, paddle-shaped teeth like those de-scribed in the Atlantic Faviidae were observed in Ple-siastrea devantieri, an Indian Ocean species recovered within clade XVII. Although this may seem surprising, Favia stelligera, a Pacific faviid also found in clade XVII, sometimes has discrete centers of rapid accre-tion as well (Budd and Stolarski, 2011). As remarked by several authors (Vaughan and Wells, 1943; Wells, 1954; Veron et al., 1977; Cheva-lier and Beauvais, 1987), it is not always easy to dif-ferentiate between pali and paliform lobes. They are ontogenetically and structurally different. Pali are de-fined as vertical structures developed along the inner axial margin of certain entosepta (Wells, 1956) and structurally identical to them. They are formed as the result of a substitution process of certain exosepta dur-ing the formation of entosepta (Wells, 1956 [Figs. 238, 241]) and composed of divergent centers of rapid ac-cretion (or trabeculae in Chevalier and Beauvais, 1987 [Figs. 322A, 332F]). Paliform lobes are the result of the detachment of offsets of the centers of rapid accre-tion from the inner edge of certain septa (Wells, 1956) and are formed from a single simple or compound center of rapid accretion (Chevalier and Beauvais, 1987 [Fig. 322C]). In practical terms, however, the distinction is not straightforward. For example, the ge-nus Goniastrea typically presents a well developed crown of palar structures. According to Wells (1956) these should be referred to as paliform lobes. Howev-er, Chevalier and Beauvais (1987) call these pali. Moreover, microstructural analyses have revealed that

similar palar morphologies are structurally different (e.g. between the genus Goniastrea and Montastraea) (Budd and Stolarski, 2011). The palar structures in P. devantieri described as paliform lobes by Veron (2000) and as pali (Veron, 2002) and observed in the holotype as well as in the other specimens examined are similar to the paliform lobes typically found in the genera Fa-via and Montastraea rather than the pali observed in P. versipora (Milne-Edwards and Haime, 1851; Vaughan and Wells, 1943; Chevalier and Beauvais, 1987). Micro-structural and molecular data provided con-cordant evidence indicating that P. devantieri is closer to, inter alia, the genera Montastraea, Goniastrea and Favia, rather than P. versipora. In other words, P. devantieri is a valid species which does not belong to the genus Plesiastrea. In addition P. versipora is mor-phologically and genetically distant from the Faviidae and monophyletic with two apparently very different taxa, Cyathelia axillaris and Trochocyathus efateensis. Both statements require further discussion and are ad-dressed hereafter.

Phylogenetic relationships of Plesiastrea versipora

On the basis of macro and microstructural features, Plesiastrea versipora is clearly distinct from the rest of the taxa presenting typical faviid micromorphology, including, as discussed, P. devantieri. Thus, the results of the species macro and micromorphology substanti-ate the previously published molecular results indicat-ing that P. versipora is not closely related to the ‘tradi-tional’ family Faviidae. What remains to be explained, at least from a morphological standpoint, is the strong-ly supported clade including P. versipora (formerly Faviidae), Cyathelia axillaris (traditionally Oculini-dae) and Trochocyathus efateensis (traditionally Cary-ophylliidae) (Kitahara et al., 2010b). It is not surprising that molecular phylogenies re-cover well supported clades including taxa with very different corallum organization and ecology (Barbei-tos et al., 2010). However, some clades are more read-ily interpretable than others. To date, perhaps the most obvious case of a monophyletic group of Scleractinia including solitary and colonial, zooxanthellate and azooxanthellate, tropical and temperate, shallow and deep species is that of the Dendrophylliidae Gray 1847. This family, however, is well characterised by a number of skeletal characters supporting the mono-phyly of this well studied group (Cairns, 2001). Con-versely, the morphological characters shared by other strongly supported clades including unexpectedly


closely related taxa such as the one including P. versi-pora, C. axillaris, and T. efateensis, are less immediate. Although one of the main goals of this study was to evaluate the monophyly of Plesiastrea rather than to examine in detail the morphologic affinities between this genus and Trochocyathus and Cyathelia, some macro morphologic features of the three genera (Fig. 9) are perhaps worth discussing in light of their close phylogenetic relationships (Kitahara et al., 2010b). The three taxa are strikingly different in terms of coral-lum condition and organization: solitary and cyathi-form in Trochocyathus (Fig. 9A), colonial and encrust-ing to massive in Plesiastrea (Fig. 9B), and colonial and dendroid formed by regular and alternate budding in Cyathelia (Fig. 9C). Corallites of T. efateensis gen-erally present 5 cycles of septa (S1-2>S3>S4>S5) (Cairns, 1999), those of C. axillaris 4 (S1-2>S3>S4) (Cairns, 1994), and of P. versipora 3 (S1≥S2>S3) (Ve-ron et al., 1977; Wijsman-Best, 1976). From an eco-logical point of view, while both T. efateensis and C. axillaris are azooxanthellate deep water corals, P. ver-sipora is a zooxanthellate reef dwelling species. How-ever, the latter is also well known for being well adapt-ed to high latitude environments (Kevin and Hudson, 1979; Veron et al., 1977; Rodriguez-Lanetty and Hoegh-Guldberg, 2002; Thomson and Frisch, 2010), to conditions of extreme temperature variations as in the Gulf (Carpenter et al., 1997; Burchard, 1979), and to the pseudo-high latitude conditions caused by cold water upwelling (Pichon et al., 2010).

Besides the presence of a papillose columella and well developed costae, the main character shared by P. versipora, C. axillaris, and T. efateensis is the number and disposition of discrete crowns of pali with respect to the number of cycles of septa (Vaughan and Wells, 1943; Chevalier and Beauvais, 1987; Cairns, 2004). In these species pali are well developed in front of each septal cycle before the last following the rule given by Milne-Edwards and Haime (1848) for the genus Plesi-astrea (‘Des pali bien développés devant tous les cy-cles cloisonnaires qui précèdent le dernier’). In Plesi-astrea P1 and P2 can be more (Fig. 284 in Veron et al., 1977) or less (Fig. 3A, 4C) differentiated as also re-marked by Milne-Edwards and Haime (1851) (‘ceux [pali] des secondaires un peu plus larges et un peu moins rapprochés du centre que ceux des primaires’). Overall, a comparison of the corallites of P. versipora with well developed and sub-equal pali with the coral-lites of the other two closely related taxa does indeed suggest similarities between the three species (Fig. 9D, E, F). As mentioned above, pali are usually interpreted as the result of the substitution of exosepta during the for-mation of entosepta (Wells, 1956 [Fig. 238]). This pro-cess explains their disposition in corals where those are only found in front of the penultimate cycle of septa, such as in the genus Caryophyllia Lamarck, 1816, and most of its close allies (Kitahara et al., 2010a, b). However, it does provide a satisfactory ex-planation in the case of corals with pali in front of each

Fig. 9. Coralla of Trochocyathus efateensis [A) side view; D) top view, images kindly provided by Marcelo V. Kitahara], Plesias-trea versipora [B) whole colony of the Hol-otype MNHN 36; E) detail of a corallite (AD021)], and Cyathelia axillaris [C) rami-fied colony (SMF C318S at EPA Socotra); F) detail of a corallite of the same speci-men]. Dashed polygons in D, E, and F con-tour similar septa and pali arrangement in T. efateensis, P. versipora, and C. axillaris, respectively.


septal cycle except for the last. In fact, the substitution model calls for a number of crown of pali equal to the number of cycles of exosepta minus one (Wells, 1956), and, hence, it would not be possible to find a crown of pali in front of S1. Rather, a second model of formation of pali described by Cuif (1968) and Chevalier and Beauvais (1987) seems to apply to the corals with pali in front of each septal cycle except for the last. Ac-cording to this model, pali are produced by successive isolation from the septa inner margin, regardless of their ento or exocoelic nature, and acquisition of a sys-tem of divergent centers of rapid accretion. A different model involving a change of pali position with the for-mation of new septa was also proposed by Lacaze-Duthiers (1897). Further analyses are needed to determine the rela-tionship between Plesiastrea, Cyathelia, and Trocho-cyathus, and possibly other taxa, on the one hand, and to clarify if further morphologic affinities can be found in the septal micromorphology on the other hand. For example, Kitahara et al. (2010a) have proposed that, on the basis of 16S rDNA, Trochocyathus and Tetho-cyathus Kühn, 1933, may be sister genera. If this was confirmed, then another deep water taxon character-ised by pali in front of each septal cycle before the last would be part of the Plesiastrea-Cyathelia-Trochocya-thus clade. A new family would perhaps have to be described. However, other genera following the same plan may well not be closely related to Plesiastrea, and, hence, additional morphological characters will have to be considered.

Phylogenetic relationships of Plesiastrea devantieri and implications for taxonomy

According to the rDNA phylogeny in this study Plesi-astrea devantieri is closely related to Goniastrea as-pera Verrill, 1905 and G. palauensis (Yabe, Sugiyama & Eguchi, 1936). However, COI results indicate that its position is unresolved in a clade including most of the Pacific faviids. Although similarities between Ple-siastrea and Montastraea have been discussed at length in the literature, and despite the fact that a few authors have also indicated similarities with Favia, no author has gone as far as discussing similarities be-tween Plesiastrea and Goniastrea. From purely morphologic standpoint, the taxa look-ing closest to P. devantieri would be some species in the genus Montastraea, such as M. curta (Fig. 1E-F) and M. annuligera. Phylogenetic relationships be-tween P. devantieri and the former species have been

investigated in this study and revealed that the two taxa are not closely related (Figs 7-8). Moreover, on the basis of the results by Huang et al. (2011) M. an-nuligera is more closely related to M. valenciennesi and different species of Favia, rather than to G. aspera and G. palauensis. Finally, the genus Montastraea is deeply polyphyletic and awaiting formal taxonomic revision (Huang et al., 2011). One of the long-standing paradigms of coral taxon-omy and systematics is that cerioid and plocoid coral-lite arrangement are informative characters (Wells, 1956). Although both P. devantieri and Goniastrea spp. are characterized by well developed crowns of paliform lobes, the plocoid condition of the former, the cerioid condition of the latter, and the different mode of calicinal budding would not have suggested phylo-genetic affinities. A revision of the genus Goniastrea does require a separate study. However, on the basis of both molecular phylogenies presented in this study, as well as in previous studies by Huang et al. (2009, 2011), the genus Goniastrea is not monophyletic, and the type species of the genus, G. retiformis, is not closely related to the two Goniastrea species which are closest to P. devantieri, namely G. aspera and G. pala-uensis. Instead, G. retiformis is closely related to Sca-pophyllia cylindrica (Milne-Edwards and Haime, 1848). Thus, while it has been shown in the present study that P. devantieri can no longer be assigned to the genus Plesiastrea, and that it should be included into the molecularly defined clade XVII (sensu Fuka-mi et al., 2008), its assignation to a different genus is not a straightforward nomenclatural process. Until a complete revision of the Robust clade, or, at least, of clade XVII, is performed and phylogenetic relation-ships are fully understood, the taxonomic position of P. devantieri remains incertae sedis. It is likely that once more taxa are added to the ex-isting molecular phylogenies of the Scleractinia, more cases of monophyletic and well supported clades of taxa with very different morphologies will be discov-ered. Then, once more, the quest for evolutionarily in-formative characters, most likely to be found or re-discovered at the skeleton micro rather then the macro scale, will be open.

Acknowledgements

The authors are grateful three anonymous reviewers for their help and constructive comments. We wish to thank E. Dutrieux (CRE OCEAN), C.H. Chaineau (Total SA), R. Hirst and M.


AbdulAziz (YLNG) for allowing and supporting our research in Yemen. Thanks to S. Basheen (Professional Divers Yemen), M.A. Ahmad and F.N. Saeed (EPA Socotra), C. Riva, S. Mon-tano, and A. Caragnano (UNIMIB) for their help in different parts of field work. Sampling in Mayotte was possible thanks to the Tara Oceans scientific expedition and the OCEANS Consortium. We are grateful in particular to E. Karsenti (EMBL) for allowing reef research during the expedition, to S. Kandels-Lewis (EMBL), and to Captain H. Bourmaud and the Tara crew in general, and to M. Oriot and J.J. Kerdraon in par-ticular. We are also indebted to L. Bigot (ECOMAR) and R. Friederich (World Courier). We are grateful to P. Muir (MTQ) for reviewing the manuscript and for images of the holotype of P. devantieri. Thanks to A. Andouche (MNHN), S. Cairns (USNM), and M. Visentini Kitahara (JCU) for specimens im-ages, and to P. Gentile (UNIMIB) for technical help with the SEM. We are grateful to E. Reynaud (Adéquation & Dével-oppement) for kindly donating part of the laboratory instru-ments for this study.

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Received: 17 March 2011Revised and accepted: 15 June 2011Published online: 30 September 2011Editor: R.W.M. van Soest

phylogeny of the coral genus plesiastrea (cnidaria ... · contributions to zoology, 80 (4) 231-249...

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